Acceptor state of monoatomic hydrogen in silicon and the role of oxygen

We determine the activation enthalpies for electron emission of two near T-site hydrogen centers in silicon to be ;0.65 and ;0.79 eV. The deeper center is oxygen related, and stabilized with a binding energy of ;0.5 eV with respect to the shallower center. We verify the negative-U behavior of both centers, and demonstrate the crucial role that this behavior and the presence of oxygen have for the migration of hydrogen in silicon. The shallower center is interpreted as the acceptor of monatomic isolated hydrogen, and the deeper center is interpreted as a perturbed version of this acceptor.